This invention relates to an electric power converting apparatus utilizing semiconductor switching elements, typically thyristors, and power diodes.
In a conventional electric power converting apparatus, such as a rectifier or inverter, a plurality of branch circuits each comprising serially connected thyristors are connected in parallel across a DC power line to form a bridge rectifier or inverter, and a DC reactor is connected in series with the power converting apparatus. As will be described later in more detail, in the thyristor converter utilizing a number of serially connected thyristors, it is necessary to connect voltage dividing circuits across respective thyristors in order to uniformly distribute or share a surge voltage among thyristors. This structure causes many problems.